The present invention relates generally to devices, systems and methods for calibration of systems such as injectors and, particularly, to devices, system and methods for pressure calibration of injectors used to inject fluid into a patient (either a human or a so-called lower animal).
In many medical diagnostic and therapeutic procedures, a physician or other person injects a patient with a fluid. Over the past several decades, a number of injector-actuated syringes and powered injectors for pressurized injection of fluids such as contrast media have been developed for use in procedures such as angiography, computed tomography, ultrasound and NMR/MRI. In many applications, these powered injectors are designed to deliver a preset amount of contrast media at a preset flow rate.
To ensure the safety of the patient, the operation of a powered injector should be carefully controlled. For example, it is desirable to not exceed a certain fluid pressure during an injection procedure. In addition to potential hazards to the patient (for example, vessel damage) and potential degradation of the diagnostic and/or therapeutic utility of the injection fluid, excessive pressure can lead to equipment failure. For example, because of the potential of cross-contamination between patients, the syringe and tubing used to carry fluid to a patient are typically changed on a per-patient basis. Such disposable syringes and other fluid path components (sometimes referred to collectively as a “disposable set”) are typically fabricated from plastics of various burst strengths. If the injector causes pressure in the fluid path to rise above the burst strength of a disposable fluid path element, the fluid path element will fail.
Direct measurement of fluid pressure in a syringe is often difficult. In controlling system or injection pressure, many currently available injectors thus use an indirect indication of syringe/system pressure. For example, motor current can be measured and related to fluid pressure through an algorithm. Likewise, force upon a component of the injector system can be measured (using, for example, a strain gauge) and similarly related to fluid pressure. Pressure measurement and control of fluid pressure are discussed, for example, in U.S. Pat. No. 5,808,203 and in Published U.S. Patent Application Nos. 2003/0171712 and 2002/0016569, assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference.
Whatever pressure measurement technique or mechanism is used to provide an estimate of fluid pressure, periodic calibration of the measurement system is required to ensure the accuracy of the measurement. Typically, an initial calibration is made at the time of manufacture and periodic calibrations are carried out thereafter. Under current practice, a technician trained in injector calibration must perform the periodic calibrations. In general a needle valve assembly is connected to the injector to simulate a “perfect syringe”. A pressure transducer is placed in fluid connection with the needle valve assembly. The technician runs the system through a testing procedure in which various known pressures are generated sequentially (for example, four individual pressures (for example, 0, 100 psi, 150 psi and 300 psi) are generated in one calibration procedure). A syringe can, for example, be filled and fluid injected into a waste container during the injection procedure. The pressure determined by the injector pressure measuring mechanism(s) is calibrated to the actual measure pressure as determined by the pressure transducer. The pressure calibration procedure can, for example, take ½ hour to an hour if no problems arise. During this time, the injector is unavailable to the medical staff. Moreover, errors or inaccuracies can be introduced by the calibrating technician. For example, among other tasks, the calibrating technician must accurately read the output of the pressure transducer at the correct time and accurately adjust the needle valve system to achieve a desired pressure.
It is desirable to develop improved calibration devices, systems and methods that reduce or eliminate the above and/or other problems with currently available sensor calibration devices, systems and methods.